Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureMedium
A network engineer is troubleshooting a multicast video distribution system. Users in different VLANs are reporting issues receiving the video stream. The multicast source is in one VLAN, and receivers are in several other VLANs. What protocol is responsible for allowing end devices to signal their interest in receiving a particular multicast stream to their local Layer 2 switch?
- AMLD
- BOSPF
- CPIM-SM
- DIGMP
Show answer & explanationAnswer & explanation
Correct answer: D. IGMP
Internet Group Management Protocol (IGMP) is used by IPv4 hosts to signal their membership in multicast groups to their local Layer 2 switch or router. This allows the switch/router to forward multicast traffic only to the interfaces where interested receivers are present, preventing unnecessary flooding.
Why the other options are wrong
- A. MLD (Multicast Listener Discovery) is the IPv6 equivalent of IGMP, used for IPv6 multicast, but the question implies IPv4 with 'multicast video distribution system' and common enterprise scenarios.
- B. OSPF (Open Shortest Path First) is an Interior Gateway Protocol (IGP) for unicast routing, not related to multicast group membership.
- C. PIM-SM (Protocol Independent Multicast - Sparse Mode) is a Layer 3 routing protocol for building multicast distribution trees, not for host-to-switch signaling.
Internet Group Management Protocol (IGMP)
A Layer 2 protocol used by IPv4 hosts to inform their local router or switch that they wish to receive multicast traffic for a specific group.
- Essential for efficient IPv4 multicast delivery.
- Prevents unnecessary flooding of multicast traffic.
- Operates between hosts and their local multicast router/switch.
Memory trick: IGMP: I've Got Multicast Preferences